In the field of medicine but also in other fields of technology there is a need for determining amounts of liquid so as to carry out an absolute liquid measurement or to dose certain amounts of liquid. For determining the amount of liquid dispensed, it is no longer the amount of liquid per se that is decisive but the change in the amount of liquid over time.
Particularly in the field of medicine there is also a strong need for liquid reservoirs for drugs. Here it is often required to administer accurately dosed amounts of liquid. In addition, there is a requirement that the liquid reservoirs are designed in a low-cost manner since they are often disposable articles which cannot be reused for hygienic reasons.
In the U.S. Pat. No. 5,463,228, an apparatus for an automatic exact dosing of small amounts of liquid in a medical analysis system is disclosed, the apparatus comprising a transparent measuring tube with a capillary tube having an internal diameter of less than 1 mm, the measuring tube further comprising a liquid transfer opening at one end of same, the liquid transfer opening being provided for drawing in a liquid. The apparatus further includes liquid phase boundary detection means for automatic detection of a liquid phase boundary in the measuring tube, an electrical position signal of a position of the liquid phase boundary being generated. The detection of the liquid phase boundary takes place in an optical manner, to be precise using a light source and a CCD line array.
In DE 4306061 A1, an apparatus for detecting the level of a capillary overflow channel is disclosed. The apparatus includes a channel connected, at one end, to an inflow which is connected to a reservoir via a controllable valve. At the other end of the channel there is a further channel of a larger diameter which is connected to an outflow. An overflow channel which is designed in a helical manner around the channel and which extends between a first detection electrode and a second detection electrode is in fluidic communication with the channel so as to capacitively detect the level of the overflow channel. The overflow channel acts as a buffer volume. If a level is detected in the overflow channel, the valve between the reservoir and the inflow is closed until it is detected that the overflow channel is empty. Then the valve is opened again until the overflow channel again has a level, whereupon the valve is closed again. The control device may be employed for separating an ink reservoir in plotter pens, recording devices, medical apparatus or apparatus used in process engineering.